This invention relates to a method and apparatus for forming a thin polymer layer on a substrate. More particularly, this invention relates to a method and apparatus for depositing a layer of a polymeric or polymerizable material having a low dielectric constant, such as parylene, on or between metal layers on a substrate containing an integrated circuit structure.
In the construction of integrated circuit structures, device geometries are constantly shrinking, resulting in an increase in parasitic capacitance between devices. Parasitic capacitance between metal interconnects on the same or adjacent layers in the circuit can result in crosstalk between the metal lines or interconnects and in a reduction of the response time. Lowering the parasitic capacitance between metal interconnects separated by dielectric material can be accomplished by either increasing the thickness of the dielectric material or by lowering the dielectric constant of the dielectric material. Increasing the thickness of the dielectric materials is, however, contrary to the goal of reducing device and structure geometries.
As a result, to reduce the parasitic capacitance between metal interconnects on the same or adjacent layers, one must change the material used between the metal lines or interconnects to a material having a lower dielectric constant than that of the materials currently used, i.e., silicon dioxide (SiO2).
Jeng et al. in xe2x80x9cA Planarized Multilevel Interconnect Scheme with Embedded Low-Dielectric-Constant Polymers for Sub-Quarter-Micron Applicationsxe2x80x9d, published in the Journal of Vacuum and Technology in June 1995, describes the use of a low dielectric constant polymeric material, such as parylene, as a substitute for silicon dioxide (SiO2) between tightly spaced conductor lines or other strategically important areas of an integrated circuit structure. Parylene, a generic name for thermoplastic polymers and copolymers based on p-xylylene and substituted p-xylylene monomers, has been shown to possess suitable physical, chemical, electrical, and thermal properties for use in integrated circuits. Formation and deposition of such polymers by the initial decomposition of a stable dimer, followed by deposition and polymerization of the resulting reactive monomer, is discussed by Ashok K. Sharma in xe2x80x9cParylene-C at Subambient Temperaturesxe2x80x9d, published in the Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 26, at pages 2953-2971 (1988). Properties of such polymeric materials, including their low dielectric constants, are further discussed by R. Olson in xe2x80x9cXylylene Polymersxe2x80x9d, published in the Encyclopedia of Polymer Science and Engineering, Volume 17, Second Edition, at pages 990-1024 (1989).
However, changing the dielectric material in the construction of integrated circuit structures from conventional silicon dioxide (SiO2) to polymeric materials cannot be accomplished using conventional methods and apparatus used to form SiO2 dielectric materials between adjacent metal lines or interconnects on a single layer or between adjacent layers of metal interconnects because the polymer deposition process involves many additional variables which must be controlled.
As a result, there is a need in the art for a controllable process and corresponding apparatus for depositing a polymer on a substrate such as an integrated circuit.
The present invention provides a method and apparatus for forming a polymer layer between metal interconnects and between layers of metal interconnects on a substrate. In particular, an apparatus and method is provided for the deposition of polymeric or polymerizable material preferably having a dielectric constant lower than that of silicon dioxide. The method and apparatus specifically provide for continuous introduction of a reactive xylylene monomer and optionally a carrier gas into a deposition chamber operated at a total pressure from 30 milliTor to 5 Torr such as a chemical vapor deposition (CVD) chamber and condensation of the monomer onto a work piece to form a parylene layer thereon. A carrier gas is preferably bubbled through a vaporizer for vaporizing a xylylene compound and the combined carrier gas and xylylene compound are passed through a furnace to decompose the xylylene into a reactive monomer.